Field of the Invention
The present invention relates to wireless telecommunications networks, and more specifically relates to systems, equipment, components, software and methods for troubleshooting signals in cellular communications networks.
Description of the Prior Art
A) Overview of Wireless Telecommunications Networks
FIG. 1 shows an overview of a typical wireless telecommunications network 2. To facilitate an understanding of the invention, the steps in carrying on a conversation between New York and California on a wireless cellular network 2 will now be explained. When the person in New York inputs on his cellular phone 4 the number of the person in California and presses “call” or “send”, a process is started to find the person in California and send a message to them to make his phone ring. When the person in California answers the call, a transmission path is set up to send and receive their conversation across the country.
For the purposes of this invention, the details of how the phone conversation is set up need not be described. This present invention is concerned with enabling the accurate recovery of a transmitted message in the section 6 of the network 2 which is linked by a radio transmitter and radio receiver. This section 6 of the network 2 is called the “Radio Access Network” which is commonly abbreviated as “RAN”. For purposes of illustration, we will describe a voice conversation. However, the same concepts apply to any other radio transmission (data, video, etc.)
B) The Radio Access Network (RAN) is the Weakest Link in a Wireless Telecommunications Network
Telecommunications is a chain of transmit and receive processes. In the case of voice conversations, human speech is received by a microphone and converted to analog signals (modulation of electromagnetic force (changes in voltage with respect to time)). The analog signals are converted to a digital representation in an analog-to-digital converter and then the digits (1s and 0s) are transported over a distance to a receiver where the 1s and 0s are converted from digital back to analog and presented to a person via a speaker. If the digital signal (1s and 0s) is not received exactly as it was transmitted, then there is distortion in the audio signal, and the person at the receiving end may not understand the conversation.
Referring again to FIG. 1, each connection between a transmitter and a receiver is commonly referred to as a “hop”. An end-to-end connection consists of several hops, each of which must correctly transmit and receive the data, through multiple Mobile Switching Centers (MSC) 7. The limiting factor in the network equipment's ability to accurately recover the signal is the signal to interference plus noise ratio (“SINR”) at the receiver. Every receiving device has an SINR at which it can no longer correctly recover the signal that was sent by the transmitter. Mathematically, the signal to interference and noise ratio is expressed as:
  SINR  =            Signal      ⁢                          ⁢      level              Interference      +              Noise        ⁢                                  ⁢        level            
where the level (amount) of the signal and the level of the noise are measured in the same units (usually power, expressed in Watts).
For each hop in the telecommunications network 2, the path between the transmitter and the receiver is called the “transmission medium” 8. In the mobile phone network 2, the transmission mediums are:                1. Transmission of pressure waves from the lips of a human talker to the microphone of a mobile phone 4 a short distance through earth's atmosphere.        2. Transmission of radio waves over-the-air from the mobile phone 4 to the radio receiver in the network 2 over distances up to approximately 10 kilometers.        3. Transmission of pulses of light through strands of glass (fiber-optic cables) 8 over distances up to approximately 100 kilometers.        4. Transmission of electrical force over electrical conductors over short distances (meters).        5. Transmission of pressure waves from the speaker of a mobile phone to the eardrums of a human listener a short distance through earth's atmosphere.        
The environment in which pressure waves are transmitted by a talker to a microphone (item 1) and from a speaker to a listener (item 5) can be a significant source of distortion in the quality of the end-to-end conversation (example: talking or listening in a crowded, noisy room). However, this SINR environment is outside the control of the Wireless Service Provider (WSP), so it is not a process the WSP tries to quantify, measure, and manage.
The transmission of electrical signals in the network (item 4) occurs over short distances (usually along a circuit path inside a piece of equipment or short distances between pieces of equipment) and are generally near 100% reliable (literally greater than 99.999% reliability).
Transmission of light pulses through fiber-optic cables occurs over long distances, but the transmission medium 8 is very good. The characteristics of the fiber-optic cables are very well known and are very stable (i.e. the characteristics have very low variability). Therefore, even though transmission of light pulses over fiber-optic cable 8 covers long distances, it can be engineered to consistently provide greater than 99.999% reliability.
The transmission medium 8 in which almost all the problems occur is the over-the-air radio wave environment. While the characteristics of radio wave transmission in free space (e.g., between the earth and the moon) are very well understood, the transmission of radio waves in the mobile phone network 2 can only be predicted statistically. There are several reasons for this:                1. The radio waves transmitted by the mobile phone 4 to the network receiver are relatively low power.        2. Radio wave transmission in the mobile phone environment does not occur in free space—it occurs in space that is filled with reflectors and absorbers (buildings, cars, people, etc. . . . ). This causes high variability in the signal level part of the SINR equation.        3. Radio waves must be transmitted on specific frequencies. If a device outside the control of the wireless service provider is broken and transmitting radio energy on the same frequency as the wireless service provider's network receiver, then this causes high variability in the interference part of the SINR equation.        4. The equipment that is used to transmit and receive radio waves over-the-air is exposed to harsh weather conditions while the equipment used for fiber-optic transmission is housed in environmentally-controlled offices. Therefore, the radio transmission and reception equipment is more prone to degradation and failure.        
The net result is that the over-the-air radio transmission environment has high variability in the signal part (numerator) of the SINR equation and sometimes also has high variability in the interference and noise part (denominator) of the SINR equation.